Multiple pump fluid delivery systems which incorporate a variable speed drive system, switchable between pumps are known. One such system is disclosed in Potter U.S. Pat. No. 5,522,707 entitled "Variable Frequency Drive System for Fluid Delivery System" assigned to the assignee hereof. The disclosure of the Potter patent is hereby incorporated by reference. The benefits of combining pumps being driven at constant speed with one being driven by a variable speed drive are known.
While useful for their intended purpose, known systems suffer from a lack of redundancy with respect to the variable speed drive. In such systems, in the event of a failure in the variable speed drive, all of the pumps must be run at constant speed and the respective pressure regulator valves relied on to deliver fluid at the preset pressure. This is a less energy efficient mode of operation.
For reasons of energy efficieny, it would be desirable, in the event of a failure of a variable speed drive, to be able to continue, in some way to vary the speed of at least some of the pumps. Preferably such functionality could be incorporated into multiple pump systems to provide both redundancy and operational flexibility.
Additionally, multiple pump fluid delivery systems which incorporate multiple variable frequency drive systems and by-pass constant-speed contactors, each dedicated to a particular pump on the system are known. The benefits of combining pumps, each being driven by an independent variable speed drive and by-pass constant-speed contactor are also known. These known systems do not incorporate pressure regulator valves to permit a preselected output pressure to be maintained.
While useful for their intended purpose, known systems suffer from a lack of redundancy with respect to the variable frequency drive. In such systems, in the event of a failure of one of the variable frequency drives, the pump with the failed drive must operate at constant-speed, and because there is no pressure regulating valve, there is then no means of delivery of the pumped fluid at the preset pressure.
It would be desirable, in the event of a variable speed drive failure, to be able in some way to run the pump with the variable speed drive failure in the constant-speed mode, while continuing to deliver the pumped fluid at the preset pressure. Preferably such functionality could be incorporated into multiple pump systems to provide both redundancy and operational flexibility.